In current conflicts, drones are increasingly being used for recognizing and attacking non-cooperative targets. Moreover, there exist numerous applications for systems of Drones in the civil sphere (fertilizer spreading in agriculture, monitoring of forest fires, Search & Rescue, event surveillance, monitoring of demonstrations). Thus, the targets sought are often located in or in proximity to civilian spaces. Moreover, it is often compulsory for the drones to pass through airspaces subject to civil air traffic control, when their takeoff/landing base is situated inside the borders of the states which dispatch them. The insertion of drones into these regulated traffic spaces is problematic since these craft do not possess the complete insertion capabilities. Furthermore, the avionics systems carrying out the flight management functions are massively located on the ground, the aircraft carrying on board only the strict minimum for short-term navigation. Consequently, these craft are bound by draconian procedures: several days' notice, escort aircraft, closure of civilian traffic during a time slot.
Currently, when the mission is not exclusively conducted in a segregated space, that is to say prohibited to civil operations, and when the communications are required between the operator of the drone and the air traffic control services, two solutions are applied. According to a first solution, the drone is used as communication relay between the operator and the controller. The operator communicates voice messages to the drone by means of analogue or digital transmission (VHF or VoIP, Voice over IP); the drone comprises a means for converting the digital voice messages into analogue voice messages so as to transmit by means of an analogue transmission of VHF (“very high frequency”), HF (“High Frequency”) type. The transmission chain in the direction from the controller to the operator is conversely identical. However, this technical solution requires the operator to have all the phraseology for communicating with the controller and consequently this task monopolizes a significant part of his attention in managing the drone. Moreover, the bandwidth necessary for digital transmission between the operator and the drone is greatly utilized for message transmission in voice format. Finally, a significant temporal latency may be introduced if the ground station of the Drone where the operator is situated is several hundred or indeed thousands of kilometers from the aircraft. According to a second solution, the operator telephones the controller directly. However, this solution involves the controller managing each drone individually and specifically. Moreover, the operator must also be responsible for all the phraseology, thus implying the same drawback aforementioned in the first solution. Having regard to the absence of any onboard pilot, it is indispensable to equip drones with more sophisticated functions assisting the ground operator in his remote management of the aircraft.
It is known to use in conventional aircraft (with onboard pilot) devices for communications by digital transmission (CPDLC for “Controller Pilot Data Link Communications”) between the pilot and the air traffic controller using standardized text messages using the vocal phraseology customarily used by an air traffic controller. These CPDLC communication systems make it possible to maintain the communication over great distances with respect to radio frequency communications and especially to reduce the operational load for dialogue between the pilot and the air traffic controller. However, CPDLC dialogue mode systems are not deployed in all airspace controls and many still communicate solely by voice messaging.